Production of Hydrogen Peroxide by Lactobacillus delbrueckii subsp. lactis as Influenced by Media Used for Propagation of Cells

ABSTRACT: Cells of Lactobacillus delbrueckii subsp. lactis I were grown in several media to determine the most suitable medium for production of H₂O₂ during refrigerated storage. H₂O₂ was detected from cells that were resuspended in phosphate buffer containing variable amounts of glucose. Cells grown in MRS broth produced more H₂O₂ during refrigerated storage than those grown in LBS pr PTM. Cells grown in LBS produced more H₂O₂ then those grown in PTM. For both MRS and LBS, cells inoculated in phosphate buffer containing 0% glucose produced significantly more H₂O₂ than those containing 1% or 10% glucose. MRS medium appears to be the best medium for growing cells for the production of H₂O₂.     

Detecting vegetable oil adulteration in hazelnut paste (Corylus avellana L.)

The possibilities of detecting hazelnut paste adulterated with refined and non-refined vegetable oils have been studied. Research was focussed mainly on peanut, high oleic-acid sunflower, corn and soybean oils which have a similar composition to hazelnut oil. The analytical procedures to detect fatty acid (FA), triacylglycerol (TAG) and tocopherol profiles as indicators of adulteration were determined. The better indicators experimentally determined were seven FA (palmitic, stearic, linoleic, linolenic, arachidonic, behenic and lignoceric acids) and different TAG with three unsaturated FA (the code letters used for FA are: P = C_16:0; S = C_18:0; O = C_18:1; L = C_18:2;; L_n = C_18:3) (LLL_n, LLL and OOO), two unsaturated FA (POL, PLL and SOO), and one unsaturated FA (PPL). As expected, when refined vegetable oils were added to hazelnut paste, the increment of stigmasta-3,5-diene allowed detection at levels of 2% oil added. Limits of detection were measured using standard and adulterated hazelnut with different amounts of non-refined vegetable oils added (5%, 10%, 20% and 30%). The distribution of tocopherols and tocotrienols is highly useful, except in the case of added sunflower oil. The differences between the experimental and theoretical values of the TAG with equivalent carbon number (ΔECN) of 42 does not improve the detection limit of hazelnut paste adulterated with peanut or sunflower oils. Similarly, tocopherols usually added to refined vegetable oils as an antioxidant were also determined.     

Natural maize phenolic acids for control of aflatoxigenic fungi on maize

ABSTRACT:  Natural phytochemicals may be an alternative to synthetic chemicals for controlling fungal growth and mycotoxin production in stored maize. A key to progress in this field is to select the best natural maize phytochemicals to be applied in a storage maize ecosystem. This research was undertaken to evaluate the effects of the natural phytochemicals trans-cinnamic acid (CA) and ferulic acid (FA) alone at concentrations of 20 to 30 mM and in 5 combinations on Aspergillus flavus Link and A. parasiticus Speare populations and aflatoxin B₁ production. Studies on Aspergillus population and aflatoxin B₁ production were carried out in maize grain in relation to a water activity a_w of 0.99, 0.97, 0.95, and 0.93. CA and FA at concentrations of 25 to 30 mM, respectively, and CA-FA mixture T9 (25 + 30 mM) were the treatments most effective at inhibiting A. flavus and A. parasiticus population at all a_w assayed after 11 d of incubation. At all a_w values, the mixture CA-FA T9 (25 + 30 mM) completely inhibited (100%) aflatoxin B₁ production by both strains at a_w= 0.99, 0.97, 0.95, and 0.93. Decreased aflatoxin B₁ levels in comparison with the control were observed with mixtures CA-FA T6 (10 + 25 mM), T7 (20 + 20 mM), and T8 (20 + 30 mM) of both strains in the majority of a_w assayed. The data show that CA and FA could be considered as effective fungitoxicants for A. flavus and A. parasiticus in maize in the a_w range 0.99 to 0.93. The information obtained shows promise for controlling aflatoxigenic fungi in stored maize.     

Microbiological Benefits of Removing Foam Formed After UV-Enhanced Ozonation of Poultry-Processing Chiller Water for Recycling

ABSTRACT: Prior experiments using 250 mL samples of unscreened poultry overflow chiller water evaluated the beneficial bactericidal and oxidative effects of 4 different treatments (namely, O₂/O₃,O₂/UV, O₂/O₃/UV, and O₂ as the control) for improving microbiological safety, turbidity, and water-use efficiency allowing its reconditioning for reuse. When excluding foam as in this present study, synergistic reductions > 1.5 log CFU/mL for aerobic plate counts (APC) were additionally achieved after 4 min for all O₃/UV treatment combinations as compared to serially applied treatments of O₃ and UV acting separately. With foam present, 16-min O₃/UV treatments were required to achieve similar results. We now report these additional benefits achieved by removing the foam formed by the advanced oxidation process of ultraviolet-photon enhanced ozonation. Furthermore, foam microbial and general physical content were analyzed to determine suitability as an additive in rendering-type processes. Treatment of the wastewater resulted in total plate counts between 2 to 4 Log CFU/mL in the foam after 8 min. Fat and protein constituted 89% of the solids collected (384 mg/L or 14% of the foam) with trace amounts of metal elements (for example, Ca, Na, K, Fe, Cu) present. Irradiating had negligible effect on foam characteristics yet decreased the amount of solids collected.     

The Effectiveness of Sanitizer Treatments in Inactivation of Salmonella spp. from Bell Pepper, Cucumber, and Strawberry

ABSTRACT: Four different postharvest treatments for removal of Salmonella from bell pepper and cucumber were examined, including washes with chlorinated water (HOCl; 200 ppm), acidified sodium chlorite (ASC; 1200 ppm), and peroxyacetic acid (PAA; 75 ppm), and treatment with gaseous chlorine dioxide (ClO₂; total 100 mg). Only ClO₂ gas was evaluated for decontamination of strawberries. Each produce was inoculated with approximately 1.0 × 10⁷ colony-forming units (CFU) of a 5-serovar cocktail of Salmonella on artificially created wounds, smooth surfaces, and stem scar tissue. For tests involving smooth surface inoculation, ASC and PAA treatments decreased contamination to undetectable levels on bell pepper and cucumber, while the chlorine treatment of bell pepper reduced contamination by approximately 2-logs. For stem scar contamination on bell pepper, ASC and PAA treatments both showed >2-log unit reductions, and chlorine treatment showed a <1-log unit reduction. For puncture wounds on bell pepper, HOCl, ASC, and PAA treatments reduced bacterial levels approximately 2-, 3-, and 1-log units, respectively, indicating that HOCl and ASC were more effective than PAA. These aqueous treatments of cucumber with puncture wounds reduced bacterial levels approximately 1-, 2-, and 2-log units, respectively. ClO₂ treatment decreased counts to undetectable levels on all inoculation sites on cucumber and on strawberry smooth surfaces, but failed to completely eliminate Salmonella from bell pepper and from the stem scar and the puncture wounds of strawberry. ASC treatment of bell pepper and ClO₂ gas treatments of cucumber showed the best efficiency for inactivation of Salmonella. ClO₂ treatments effectively reduced Salmonella cells inoculated on the smooth surface and stem scar of strawberries compared with unsanitized control.     

Sensory Evaluation of Ground Beef Stored in High-oxygen Modified Atmosphere Packaging

ABSTRACT: The quality of ground beef stored in high-oxygen modified atmosphere packaging (MAP) (80% O₂ and 20% CO₂) was evaluated and compared to controls stored in oxygen-impermeable chubs. Patties were formed from the stored ground meat at d 1, 6, and 10. Color, microbial load, thiobarbituric acid (TBA) number, and sensory acceptability were measured. Patties from both treatments bloomed to red with a* values > 16. Aerobic plate counts increased to 9 × 10⁵CFU/gby 10 d storage, but were not different (p < 0.05) between treatments. TBA number of high-oxygen samples increased to 2.1 after 10 d, compared to 0.8 for controls. The flavor of samples in high-oxygen were rated less desirable after 6 or 10 d.     

Chemical, Microbiological, and Sensory Quality of Cod Products Salted in Different Brines

ABSTRACT: Studies were carried out on the effect of different brines containing high concentrations of calcium chloride (CaCl₂, 0.8%w/w), magnesium chloride (MgCl₂, 0.4%w/w), and potassium chloride (KCl, 50%) on the chemical (chloride and moisture contents), microbial (total viable counts, total coliforms, enterococci, and staphylococci), and sensory quality of salted cod. The brines were prepared from combinations of the Ca, Mg, and K ions and sodium chloride (NaCl) at pH 6.5 and 8.5. Additionally, 3 salts (one composed solely of NaCl, another commercial sea salt from the southern Europe and, finally, a natural salt from northern Europe) were also tested. Principal component analysis structured the chemical and microbiology data in 3 clusters: (1) an extreme cluster, formed by cod brined in the commercial sea salt, which achieved the highest microbiological counts, namely 4.1 log CFU/g on plate count agar (PCA) and 1250 coliforms/g; (2) an intermediate cluster composed of cod salted in brine containing 50% NaCl, 0.4% MgCl₂, and 49.6% KCl (pH 6.5); and (3) a central cluster, including all the other treatments, which presented the lowest microbiological counts, namely 2.4 log CFU/g on PCA and 20 coliforms/g. Although the batches of the intermediate cluster presented slightly higher total viable and staphylococci counts than the central cluster, the presence of Mg and K ions improved the color of the salted product. In the assayed concentrations, CaCl₂, MgCl₂, and KCl can be used in the brining of cod without adversely affecting the microbiological and sensory quality of the salted cod.     

Lethal and Sublethal Action of Acetic Acid on Salmonella In Vitro and on Cut Surfaces of Apple Slices

ABSTRACT Antimicrobial action of acetic acid (AA) on Salmonella as affected by acid concentration, exposure time, culture age, and bacterial strains was investigated. Relative susceptibility of 6 Salmonella serovars to AA action was in the following order: S. bareilly > S. typhimurium > S. montevideo > S. poona > S. mbandaka > S. stanley. The stationary-phase cells of S. mbandaka were 100-fold more resistant to AA action than the log-phase cells. A mixture of Salmonella strains at a specified physiological stage should be used when testing the efficacy of the sanitizer treatment. Washing apple disks with NaOCl, H₂O₂, AA, or Na₃P0₄ greatly reduced the number of Salmonella and 30% to 40% of cells that survived were injured. Washing with a mixture of AA and H₂O₂ was the most effective in removing Salmonella from apple disks.     

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON THE QUALITY OF SMOKED CATFISH

Smoked catfish were inoculated with Listeria ivanovii then packaged under 80% CO₂/20% N₂ (M₁) and 40% CO₂/30%O₂/130% N₂ (M₂) and stored at 2 and 8C. Noninoculated samples packaged under air (A) served as controls. Fillets stored under M₂ at 8C showed the fastest growth of L. ivanovii. L. ivanovii counts in samples stored under M₁ at both temperatures decreased significantly over time. Listeria growth was observed in samples stored under air at 2 and 8C after 2 weeks. APC results were similar to that of Listeria The highest TBA values were observed in M₂-stored samples followed by air-stored samples. Lightness ("L" values) increased significantly, whereas "a" (redgreen) and "b" (blue/yellow) values decreased in all atmospheres at both temperatures over time. The combined use of M₁ and 2C improved the quality of smoked catfish by inhibiting microbial growth and minimizing the extent of lipid oxidation.     

SUPERCRITICAL CARBON DIOXIDE TREATMENT TO INACTIVATE AEROBIC MICROORGANISMS ON ALFALFA SEEDS

The supercritical carbon dioxide (SC-CO₂) process involves pressurizing CO₂ in a chamber which generates liquid phase of carbon dioxide. Pressurized liquid CO₂ has a strong extraction capability of organic and inorganic compounds. The recent studies have also demonstrated that antimicrobial effect of SC-CO₂ due extraction some cellular components of microorganisms. The efficacy of a supercritical carbon dioxide treatment on alfalfa seeds contaminated with Escherichia coli K12 was tested at 2000, 3000, and 4000 psi at 50C. Samples were treated for 15, 30, and 60 min at each pressure. After pummeling the seed samples in 0.1% peptone water, the initial and final Escherichia coli and total aerobic bacteria on the seeds were determined by plating on 3M Petri Films. After 48 h of incubation at 37 C, the colonies were enumerated. Treated seeds were evaluated in terms of germination characteristics. For aerobic plate count, the effect of pressure in the range of 2000–4000 psi was not statistically significant (p > 0.05) even though 85.6% inactivation was achieved at 4000 psi for 60 min. For E. coli, the reductions for 2000, 3000, and 4000 psi treatments for 15 min were 26.6, 68.1, and 81.3%, respectively. As the time was increased from 15 to 60 min at 4000 psi, the percent E. coli reduction increased from 81.3% to 92.8%. The percent germination for all treatments was over 90%. There was no significant difference (p > 0.05) in the germination rate of treated and untreated seeds. Supercritical carbon dioxide treatments demonstrated a reduction of E. coli K12 and total aerobic counts without affecting the germination characteristics of alfalfa seeds (p < 0.05). This study was a step in the direction of improving safety of alfalfa seeds used to produce fresh sprouts, which have been the cause of several outbreaks.     

MICROBIAL CHANGES ON FRESHLY SLAUGHTERED PORK CARCASSES DUE TO "HOT" LACTIC ACID DECONTAMINATION

We studied the microbial changes on fresh (still warm) pork carcasses immediately after electrostatic spraying of lactic acid solutions and during chilled storage. Lactic acid decontamination (LAD) included electrostatic spraying of hot (55C) solutions of 1% lactic acid for 90 s and 2%- and 5% lactic acid for 30 and 90 s. The treatments increased the carcass surface temperature from 22C to about 32–43C. The bactericidal activity of lactic acid killed mainly Gram-negative bacteria. Reductions in "total" psychrotrophic Gram-negative and Entero-bacteriaceae counts were found reliable indicators for the efficacy of LAD. Hot 2–5% LAD treatments achieved overall reductions in Gram-negative psychrotrophs ranging from 0.8 to more than 1.4 log₁₀ cfu per cm². Overall reductions in mesophilic Enterobacteriaceae counts ranged from approximately 1.2 to more than 1.8 log₁₀ cfu per cm². Treatments with 1% lactic acid achieved marginal 0.5–0.6 overall log₁₀ reductions in these groups of organisms. Bactericidal effects after LAD occurred during a lag period of whose duration increased with the lactic acid concentration of the spray solution. The lag lasted less than 1 day on 1% LAD, 2 days on 2% LAD and 4 days on 5% LAD meat. During these lags the meat surface pH rose from pH 2.7 to 3.2 immediately after LAD to pH 4.8 to 5.2. During aerobic chilled storage after LAD the growth of Gram-negative psychrotrophs was controlled only temporarily. These organisms became the dominant group of organisms. The practical utility of electrostatic spraying of fresh pork carcasses with hot 1–5% LAD to improve the keeping quality is questionable .     

Physicochemical Properties and Microbial Stability of Reduced-Fat Chinese-Style Sausage Stored under Modified Atmosphere Systems

ABSTRACT: Physicochemical properties and microbial stability of reduced-fat Chinese-style sausages packaged with various modified atmosphere packaging (MAP) systems were evaluated. With the exception of VAC (vacuum) treatment, the TBARS (thiobarbituric acid-reactive substances) values increased with increasing storage time. Treatments of C100 (100% CO₂), C80 (80% CO₂/20% N₂), and C20 (20% CO₂/80% N₂) were higher in TBARS values than VAC and N2 (100% N₂) after 2 wk of storage. The numbers of total plate counts, psychrotrophs, total anaerobes, or lactic acid bacteria increased slightly, though statistically insignificant, during storage, while N2 was numerically the lowest and VAC was intermediate. Vacuum packaging was more effective than other MAP in maintaining lipid and microbial stability of reduced-fat Chinese-style sausage. Keywords: reduced-fat, Chinese-style sausage, MAP, storage stability, vacuum packaging     

Formulation Protocol and Dicationic Salts Affect Protein Functionality of Model System Beef Batters

ABSTRACT: The objective of this study was to determine if addition, and order of addition, of CaCl₂ and MgCl₂ affected protein functionality of lean beef preblends. Four treatments were applied to non-preblended (NPB) batters prior to thermal processing. Six treatments were applied to preblended (PB) batters 12 h prior to thermal processing. All treatments contained 2% NaCl. Dicationic salts decreased raw pH in NPB and PB batters, while cooked pH was unaffected. Magnesium chloride in NPB and CaCl₂+ MgCl₂ in PB batters resulted in the highest total soluble protein (TSP). Calcium chloride + MgCl₂ in NPB batters resulted in firmer gels compared to the control. Magnesium chloride, in both NPB and PB, caused the greatest increase in soluble myosin, and preblending decreased myosin solubility.     

Improved Sanitizing Treatments for Fresh Tomatoes

ABSTRACT:  Fresh tomatoes repeatedly have been associated with major outbreaks of salmonellosis; however, efforts to disinfect them with chlorine or other sanitizing agents have had only mixed success. Our objective was to determine whether hydrogen peroxide (H₂O₂) treatments would be more efficacious than conventional methods in disinfecting tomatoes containing human pathogens and, at the same time, be noninjurious to quality. Tomatoes were dip inoculated with Escherichia coli NRRL B-766 or a Salmonella cocktail and then held for 0, 24, or 48 h at 4 or 24 °C prior to treatment. Treatments included 200 ppm chlorine (Cl₂) at 20 °C for 3 min, water at 20 °C for 3 min or at 60 °C for 2 min, 1% H₂O₂ at 20 °C for 15 min or at 60 °C for 2 min, and 5% H₂O₂ at 60 °C for 2, 3, or 5 min. In tomatoes held 48 h postinoculation, the chlorine treatment was only marginally more effective than an equivalent water rinse in reducing the target bacterial population, while the hot water and 1% H₂O₂ treatments achieved reductions no greater than 1.3 logs. However, application of 5% H₂O₂ at 60 °C resulted in larger reductions. Efficacy of all treatments decreased as the time interval between inoculation and treatment increased. Greater reductions could not be achieved with 5% H₂O₂ at 60 °C by increasing the contact time or addition of surfactants, and these treatments caused some quality loss.     

APPLICATION OF CHLORINE TO REDUCE POPULATIONS OF ESCHERICHIA COLI ON BEEF

The effects of chlorine against 2 strains of E. coli attached to the surface of beef carcass tissue (BCT) were examined using a model carcass washer. Lean and adipose BCT with approximately 5 log ₁₀ CFU/cm ² E. coli bacteria were spray-treated with water and sodium hypochlorite (NaOCl) to give chlorine concentrations of 50, 100, 250, 500, or 800ppm, incubated for 24 h, 4C, and E. coli populations enumerated. Spray treatments with water did significantly (P < 0.05) reduce the bacterial populations of either organism attached to lean or adipose BCT, as compared to populations of controls; however, reductions were less than 0.60 log ₁₀ CFU/cm ². Treatments with 500 and 800 ppm chlorine against E. coli ATCC 25922 attached to BCT resulted in the greatest reductions of 1.22 and 1.28 log ₁₀ CFU/cm ², respectively. At 800 ppm chlorine , E. coli O157:H7 ATCC 43895 attached to BCT was reduced by 1.04 log ₁₀ CFU/cm ², whereas spray treatments with 50, 100, 250, and 500 ppm chlorine resulted in reductions of < 1 log ₁₀ CFU/cm ². Spray treatments with chlorine from sodium hypochlorite solutions reduced populations of E. coli, however, these reductions were not sufficient to completely inactivate the bacteria attached to red meat .     

Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N₂ or without flushing with N₂, lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1–1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly ( P > 0.05). Flushing packages of lettuce with 100% N₂ followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2–3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua , strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes , it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N₂ flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.     

PHYSICAL AND MICROBIAL CHARACTERISTICS OF PORK LOINS IN MODIFIED ATMOSPHERE PACKAGES

Bone-in pork loins (n = 45) were selected from a commercial facility, subjected to one of three gas flush packaging treatments: NC: 75% N₂, 25% CO₂; ONC₁: 45% 0₂, 35% N₂, 20% CO₂; ONC₂: 66% O₂, 9% N₂, 25% CO₂, and stored for 7, 14 or 21 days at 0±2C. After storage, treatment and storage effects on visual evaluations, storage characteristics, microbial analysis and retail display characteristics were determined. The ONC¹ and ONC²treated loins had less discoloration after 21 days than NC treated loins, and NC treated chops had the least desirable retail display characteristics (P < 0.05). Fewer (P < 0.05) lactic acid producing bacteria (day 21) were found on NC treated loins, resulting in chops with a shorter retail shelf-life. These results indicate that higher oxygen levels (45 and 66%) are necessary for the modified atmosphere storage of fresh pork loins for 21 days.     

Efficacy of Sulfuric Acid Scarification and Disinfectant Treatments in Eliminating Escherichia coli O157: H7 from Alfalfa Seeds Prior to Sprouting

ABSTRACT: E. coli O157:H7 reduction on inoculated alfalfa seeds was investigated using acid scarification treatments with or without subsequent application of sanitizers. Scarification with 0.1 to 2N H₂SO₄ for 2.5 to 45 min did not affect (p ≤ 0.05) seed viability. E. coli O157:H7 was reduced by 2.1 to 5.0 logs after treating with 0.1 to 2N H₂SO₄ for 5 to 20 min. Combined scarification (0.5N H₂SO₄) and H₂O₂ or CH₃COOH treatments enhanced microbial destruction by less than 1 log compared to sanitizer alone. Chlorine, Na₂CO₃, or Na₃PO₄ treatments preceded by scarification did not significantly increase microbial destruction compared to sanitizer alone. Appreciable reductions in seed germination were only observed with chlorine treatments.     

Saccharomyces cerevisiae strains AWRI 838, Lalvin EC1118 and Maurivin PDM do not produce excessive sulfur dioxide in white wine fermentations

The formation of sulfur dioxide (SO₂) by the related Saccharomyces cerevisiae strains AWRI 838, Lalvin EC11 18 and Maurivin PDM has been determined in white wines produced by laboratory-scale fermentation. Three different preparations of these strains, available for vinification in 1995, were indistinguishable based on production of SO₂. None of the physico-chemical factors investigated could stimulate an over-production of SO₂, and any changes in its concentration were independent of juice pH, sugar content, exposure to air, clarity, initial concentration of SO₂, and grape variety. Only fermentation without exposure to air could affect the concentration of SO₂, reducing it by 13–15% in the final wines. Under the conditions tested, changes in the concentration of SO₂ in wines produced with AWRI 838 and related strains would not account for wines which resist malolactic fermentation.     

Low Temperature Growth of Type E Clostridium botulinum Spores. 1. Effects of Sodium Chloride, Sodium Nitrite and pH

SUMMARY— The effects of pH and the addition of sodium chloride (NaCl) or sodium nitrite (NaNO₂) to trypticase-peptone-glucose (TPGI and trypticase-peptone-sucrose-yeast extract (TPSY) media upon spore outgrowth were investigated using seven Type E Clostridium botulinum strains. An inoculum of 1.0 × 10⁵ spores/ml was used and the pH was adjusted with hydrochloric acid to cover the range of 5.2 to 6.6. To define salt tolerance, NaCl was added to the media at intervals of 0.5% in the range of 2.0 to 5.0% and at 0.1% intervals in the 4.5 to 5.0% range. The effect of NaNO₂ was investigated with the addition of 100 and 200 ppm NaNO₂ to the media. Samples were incubated at 30, 15.6, 10, 7.2, 5.0 and 3.4°C. Outgrowth of all strains tested was inhibited at pH 5.2 at 15.6°C. Inhibition occurred at higher pH at lower temperatures. None of the strains showed outgrowth with 4.87% NaCl in the media at any of the incubation temperatures used. Addition of 100 and 200 ppm NaNO₂ to the media inhibited the outgrowth of the Minneapolis, 517, 26080 and A6247 strains but not the Kalamazoo and Seattle Forks strains.